Why should I be sad?

Last couple of days I found myself preoccupied with thoughts of the future and past.I have been getting better at living in the moment but out of curiosity I drifted from this philosophy momentarily. Like a drug addict in relapse I missed the chemical fix I would get from dwelling in emotions of despair and loneliness. Suffering seems to bring out this aliveness out of us while happiness does it just as well. Chaos, unpredictability, curiosity; show me the way into discontentment. Sitting on a bench, happiness overwhelmed me. It was that very second I got back into the moment and realized the answer to my troubling question. Its the sense of contentment that we must avoid at all cost for it will leave you feeling lifeless, a gear in a ghost machine.